1. Field of the Invention
The present invention relates to a dashboard insulator for a motor vehicle suitable for reduction of a noise generated in a compartment of the motor vehicle by propagation into the compartment and a manufacturing method therefor.
2. Description of the Related Art
As this type of the dashboard insulator, a soundproof material for a motor vehicle described in Japanese Patent Laid-Open Publication No. 2001-347900 is proposed. The soundproof material is constructed by layering a first sound absorption layer of air permeability, a resin layer of air impermeability, and a second sound absorption Layer of air permeability sequentially.
The soundproof material thus constructed is disposed along a dash panel which separates the compartment from an engine room of the motor vehicle. Herein, in the soundproof material, the first sound absorption layer of air permeability is disposed so as to be located inside the compartment for absorbing noises in the compartment, while the second sound absorption layer of air permeability is disposed so as to be located inside the engine room for absorbing noises from the engine room. Also, the resin layer of air impermeability is laminated between the first and second sound absorption layers of air permeability so as to be located opposing against the engine room by way of the second sound absorption layer of air permeability thereby to insulate propagation of the noises from the engine room to the compartment.
In the soundproof material as constructed above, the first and second sound absorption layers have permeability respectively. However, the resin layer of air impermeability does not have air permeability at all.
Therefore, even though the resin layer of air impermeability insulates the noises from the engine room to the compartment through the first sound absorption layer of air permeability, the resin layer of air impermeability exerts a sound insulating function also against the noises into the compartment from the outside thereof. In other words, because the soundproof material includes the resin layer of air impermeability, it is difficult that the soundproof material absorbs the noises generated in the compartment due to propagation into the compartment from the outside thereof, even if the noises may be reflected by the above-mentioned sound insulating function within the compartment.